Switch based on phase-change material

ABSTRACT

The present description concerns a switch based on a phase-change material comprising: a region of the phase-change material; a heating element electrically insulated from the region of the phase-change material; and one or a plurality of pillars extending in the region of the phase-change material, the pillar(s) being made of a material having a thermal conductivity greater than that of the phase-change material.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the priority benefit of French patentapplication number 2207296 (for 21-GR4-0974US01)/2207297 (for22-GR4-0006US01)/2207298 (for 21-GR4-0951US01), filed on Jul. 18, 2022,entitled “Commutateur à base de matériau à changement de phase”, whichis hereby incorporated by reference to the maximum extent allowable bylaw.

BACKGROUND Technical Background

The present disclosure generally concerns electronic devices. Thepresent disclosure more particularly concerns switches based on aphase-change material capable of alternating between a crystal phase,electrically conductive, and an amorphous phase, electricallyinsulating.

Description of the Related Art

Many applications taking advantage of switches, or interrupters, basedon a phase-change material to allow or prevent the flowing of anelectric current in all or part of a circuit are known. Such switchesmay particularly be implemented in radio frequency communicationapplications, for example, to switch an antenna between transmit andreceive modes, to activate a filter corresponding to a frequency band,etc.

BRIEF SUMMARY

There is a need to improve existing switches based on a phase-changematerial and their manufacturing methods.

An embodiment overcomes all or part of the disadvantages of knownswitches based on a phase-change material and of their manufacturingmethods.

An aspect of an embodiment more particularly aims at providing a switchhaving an improved thermal efficiency.

An aspect of another embodiment more particularly aims at providing aswitching having decreased dimensions.

An aspect of still another embodiment more particularly aims atproviding a switch having an increased switching speed.

For this purpose, an embodiment provides a switch based on aphase-change material comprising:

-   -   a region made of said phase-change material;    -   an electrically-heating element insulated from the region of        said phase-change material; and    -   one or a plurality of pillars extending in the region of said        phase-change material, the pillar(s) being made of a material        having a thermal conductivity greater than that of said        phase-change material.

According to an embodiment, the material of the pillar(s) iselectrically insulating.

According to an embodiment, the material of the pillar(s) is selectedfrom among aluminum nitride or silicon nitride.

According to an embodiment, said phase-change material is a chalcogenidematerial.

According to an embodiment, an electrically insulating layer isinterposed between the heating element and the region of saidphase-change material.

According to an embodiment, the electrically insulating layer is made ofthe same material as the pillar(s).

According to an embodiment, the region of said phase-change material iscloser to a substrate, inside and on top of which is formed the switch,than the heating element.

According to an embodiment, the heating element is closer to asubstrate, inside and on top of which is formed the switch, than theregion of said phase-change material.

According to an embodiment, the region of said phase-change material iscoated with a passivation layer.

According to an embodiment, the region of said phase-change materialcouples first and second conduction electrodes of the switch.

According to an embodiment, each pillar has a maximum lateral dimensionequal to approximately 300 nm.

According to an embodiment, each pillar is separated from theneighboring pillars by a distance in the order of 300 nm.

Further, an embodiment provides a switch based on a phase-changematerial comprising:

-   -   a region of said phase-change material coupling first and second        conduction electrodes of the switch;    -   an electrically-heating element insulated from the region of        said phase-change material; and    -   one or a plurality of islands made of an electrically insulating        material each having a first surface extending on top of and in        contact with the first and second electrodes, wherein the region        of said phase-change material extends on sides and on a second        surface, opposite to the first surface, of each island.

According to an embodiment, said sides of each island are substantiallyparallel to a conduction direction of the switch.

According to an embodiment, the switch comprises a single island made ofsaid electrically insulating material.

According to an embodiment, the switch comprises a plurality of islandsmade of said electrically insulating material.

According to an embodiment, the islands are distributed at regularintervals along the heating element.

According to an embodiment, said electrically insulating material isaluminum nitride.

According to an embodiment, an electrically insulating layer, interposedbetween the region of said phase-change material and the heatingelement, coats all the sides of each island.

According to an embodiment, the region of said phase-change materialcoats all the sides of each island.

According to an embodiment, an electrically insulating layer, interposedbetween the region of said phase-change material and the heatingelement, coats the upper surface and the sides of the region of saidphase-change material.

According to an embodiment, each island has a cross-section oftrapezoidal shape.

According to an embodiment, each island has a height equal toapproximately 5 μm.

According to an embodiment, the switch further comprises one or aplurality of pillars extending in the region of said phase-changematerial, the pillar(s) being made of a material having a thermalconductivity greater than that of said phase-change material.

An embodiment provides a method of forming a switch such as described,comprising a step of forming of the island(s) on top of and in contactwith a portion of the upper surface of each control electrode.

Further, an embodiment provides a switch based on a phase-changematerial comprising:

-   -   first and second regions made of said phase-change material each        connected to first and second conduction electrodes of the        switch, the second region being located above the first region;        and    -   a heating element located between the first and second regions        of said phase-change material and electrically insulated from        the first and second regions of said phase-change material.

According to an embodiment, a region, among the first and second regionsof said phase-change material, is on top of and in contact with thefirst and second electrodes.

According to an embodiment, the other region of said phase-changematerial is connected to the first and second electrodes by vias.

According to an embodiment, said vias are in contact, by their uppersurface, with the lower surface of said other region of saidphase-change material.

According to an embodiment, the other region of said phase-changematerial is under and in contact with third and fourth electrodes.

According to an embodiment, the third and fourth electrodes arerespectively connected to the first and second electrodes by vias.

According to an embodiment, the heating element is made of metal or of ametal alloy.

According to an embodiment, the heating element is made of tungsten orof titanium nitride.

According to an embodiment, the switch further comprises one or aplurality of pillars extending in the first region of said phase-changematerial, the pillar(s) being made of a material having a thermalconductivity greater than that of said phase-change material.

According to an embodiment, the switch further comprises one or aplurality of pillars extending in the second region of said phase-changematerial, the pillar(s) being made of a material having a thermalconductivity greater than that of said phase-change material.

An embodiment provides a method of manufacturing a switch such asdescribed, comprising the following successive steps:

-   -   a) deposition of the first region of said phase-change material;    -   b) forming of the heating element; and    -   c) deposition of the second region of said phase-change        material.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other features and advantages of the presentdisclosure will be discussed in detail in the following non-limitingdescription of specific embodiments in connection with the accompanyingdrawing, in which:

FIG. 1 is a simplified and partial perspective view of an example of aswitch based on a phase-change material;

FIG. 2 is a cross-section view, along plane AA of FIG. 1 , of the switchof FIG. 1 ;

FIG. 3 is a simplified and partial perspective view of an example of aswitch based on a phase-change material according to an embodiment;

FIG. 4 is a cross-section view, along plane AA of FIG. 3 , of the switchof FIG. 3 ;

FIG. 5 is a simplified and partial perspective view of an example of aswitch based on a phase-change material according to an embodiment;

FIG. 6A, FIG. 6B, and FIG. 6C illustrate, in simplified and partialcross-section views, successive steps of an example of a method ofmanufacturing the switch of FIG. 3 according to an embodiment;

FIG. 7 is a simplified and partial perspective view of an example of aswitch based on a phase-change material according to an embodiment;

FIG. 8 is a cross-section view, along plane AA of FIG. 7 , of the switchof FIG. 7 ;

FIG. 9 is a simplified and partial perspective view of an example of aswitch based on a phase-change material according to an embodiment;

FIG. 10 is a simplified and partial perspective view of an example of aswitch based on a phase-change material according to an embodiment;

FIG. 11 is a simplified and partial perspective view of an example of aswitch based on a phase-change material according to an embodiment;

FIG. 12A and FIG. 12B illustrate, in simplified and partialcross-section views, successive steps of an example of a method ofmanufacturing a switch based on a phase-change material according to anembodiment;

FIG. 13A, FIG. 13B, FIG. 13C, and FIG. 13D illustrate, in simplified andpartial cross-section views, successive steps of an example of a methodof manufacturing a switch based on a phase-change material according toan embodiment; and

FIG. 14A and FIG. 14B illustrate, in simplified and partialcross-section views, successive steps of an example of a method ofmanufacturing a switch based on a phase-change material according to anembodiment.

DETAILED DESCRIPTION

Like features have been designated by like references in the variousfigures. In particular, the structural and/or functional features thatare common among the various embodiments may have the same referencesand may dispose identical structural, dimensional and materialproperties.

For the sake of clarity, only the steps and elements that are useful foran understanding of the embodiments described herein have beenillustrated and described in detail. In particular, the circuits forcontrolling switches based on a phase-change material and theapplications where such switches may be provided have not been detailed,the described embodiments and variants being compatible with usualcircuits for controlling switches based on a phase-change material andwith usual applications implementing switches based on a phase-changematerial.

Unless indicated otherwise, when reference is made to two elementsconnected together, this signifies a direct connection without anyintermediate elements other than conductors, and when reference is madeto two elements coupled together, this signifies that these two elementscan be connected or they can be coupled via one or more other elements.

In the following description, when reference is made to terms qualifyingabsolute positions, such as terms “front”, “back”, “top”, “bottom”,“left”, “right”, etc., or relative positions, such as terms “above”,“under”, “upper”, “lower”, etc., or to terms qualifying directions, suchas terms “horizontal”, “vertical”, etc., it is referred unless specifiedotherwise to the orientation of the drawings.

Unless specified otherwise, the expressions “about”, “approximately”,“substantially”, and “in the order of” signify plus or minus 10%,preferably of plus or minus 5%.

FIG. 1 is a simplified and partial perspective view of an example of aswitch 100 based on a phase-change material. FIG. 2 is a cross-sectionview, along plane AA of FIG. 1 , of the switch 100 of FIG. 1 . Plane AAof FIG. 1 is substantially parallel to a conduction direction of switch100.

In the shown example, switch 100 is formed inside and on top of asubstrate 101, for example, a wafer or a piece of wafer made of asemiconductor material. As an example, substrate 101 is made of siliconand has a resistivity in the order of 100 Ω·m (silicon said to have a“high resistivity”).

In this example, substrate 101 is coated on one of its surfaces (itsupper surface, in the orientation of FIG. 2 ) with an electricallyinsulating layer 103. As an example, layer 103 is made of silicondioxide (SiO₂) and has a thickness in the order of 500 nm.

In the shown example, switch 100 comprises first and second conductionelectrodes 105 a and 105 b located on top of and in contact with theupper surface of electrically insulating layer 103. Electrodes 105 a and105 b are for example intended to be connected to a radio frequencycommunication circuit, not detailed in the drawings. A distance forexample in the order of 1 μm separates electrode 105 a from electrode105 b. Electrodes 105 a and 105 b are made of a conductive material, forexample, a metal, for example, copper or aluminum, or of a metal alloy.Each electrode 105 a, 105 b may have a monolayer structure or amultilayer structure comprising for example, from the upper surface oflayer 103, a titanium layer having a thickness in the order of 10 nm, alayer of a copper and aluminum alloy having a thickness in the order of440 nm, another titanium layer having a thickness in the order of 10 nm,and a titanium nitride layer (TiN) having a thickness in the order of100 nm.

In this example, another electrically insulating layer 107 coatsportions of the upper surface of layer 103 not coated with electrodes105 a and 105 b. In the illustrated example, the material of layer 107surrounds electrodes 105 a and 105 b on all their lateral surfaces. Aportion of layer 107 extends in particular between electrodes 105 a and105 b and electrically insulates electrode 105 a from electrode 105 b.Layer 107 is for example flush with the upper surface of electrodes 105a and 105 b, as illustrated in FIG. 2 . As an example, layer 107 is madeof the same material as layer 103, for example, silicon dioxide.

To avoid overloading the drawing, substrate 101 and electricallyinsulating layers 103 and 107 have not been shown in FIG. 1 .

In the shown example, switch 100 further comprises a region 109 made ofa phase-change material coupling the first and second conductionelectrodes 105 a and 105 b. More precisely, in this example, region 109coats the upper surface of the portion of layer 107 separatingconduction electrodes 105 a and 105 b and further extends, for exampleover a distance in the order of 1 μm, on top of and in contact with aportion of the upper surface of each electrode 105 a, 105 b. Region 109for example has a thickness T in the range from 100 to 300 nm.

As an example, region 109 of switch 100 is made of a material called“chalcogenide”, that is, a material or an alloy comprising at least onechalcogen element, for example, a material from the family of germaniumtelluride (GeTe), of antimony telluride (SbTe), or ofgermanium-antimony-tellurium (GeSbTe, commonly designated with acronym“GST”). As a variant, region 109 is made of vanadium oxide (VO₂).

Generally, phase-change materials are materials capable of alternating,under the effect of a temperature variation, between a crystal phase andan amorphous phase, the amorphous phase having an electric resistancegreater than that of the crystal phase. In the case of switch 100,advantage is taken of this phenomenon to obtain an off state, preventingthe flowing of a current between conduction electrodes 105 a and 105 b,when a portion at least of the material of region 109 located betweenthe conduction electrodes is in the amorphous phase, and an on state,allowing the flowing of the current between electrodes 105 a and 105 b,when the material of region 109 is in the crystal phase.

In the shown example, the upper surface of region 109 is coated with anelectrically insulating layer 111. As an example, layer 111 is made of adielectric and thermally conductive material, for example, siliconnitride (SiN) or aluminum nitride (AlN).

In this example, switch 100 further comprises a heating element 113located on top of and in contact with the upper surface of layer 111,vertically in line with region 109 of phase-change material. Heatingelement 113 is electrically insulated from region 109 by layer 111. Inthe shown example, heating element 113 has the shape of a stripextending along a direction substantially orthogonal to the conductiondirection of switch 100. In this example, the ends of heating element113 are respectively connected to third and fourth control electrodes115 a and 115 b of switch 100 by means of conductive pads 117. Heatingelement 113 for example has a thickness in the order of 100 nm. As anexample, heating element 113 is made of a metal, for example, tungsten,or of a metal alloy, for example, titanium nitride.

Although this has not been illustrated in the drawings, the structure ofswitch 100 may be coated, on the upper surface side of substrate 101,with a thermally insulating layer intended to confine the heat generatedby heating element 113.

During switchings between on and off state, the control electrodes 115 aand 115 b of switch 100 are for example intended to be submitted to acontrol voltage causing a current flow through heating element 113. Thiscurrent causes, by Joule effect and then by radiation and/or conductioninside of the structure of switch 100, particularly through layer 111, atemperature rise of region 109 from its upper surface, located in frontof heating element 113.

More precisely, to toggle switch 100 from the off state to the on state,region 109 is heated by means of heating element 113, for example, at atemperature T1 and for a duration d1. Temperature T1 and duration d1 areselected to cause a phase change of the material of region 109 from theamorphous phase to the crystal phase. Temperature T1 is for examplehigher than a crystallization temperature and lower than a meltingtemperature of the material of region 109. As an example, temperature T1is in the range from 150 to 350° C. and duration d1 is shorter than 1μs. In the case where region 109 is made of germanium telluride,temperature T1 is for example equal to approximately 300° C. andduration d1 is for example in the range from 100 ns to 1 μs.

Conversely, to toggle switch 100 from the on state to the off state,region 109 is heated by means of heating element 113, for example up toa temperature T2 higher than temperature T1, and for a duration d2shorter than duration d1. Temperature T2 and duration d2 are selected tocause a phase change of the material of region 109 from the crystalphase to the amorphous phase. Temperature T2 is for example higher thanthe melting temperature of the phase-change material. As an example,temperature T2 is in the range from 600 to 1,000° C. and duration d2 isshorter than 500 ns. In the case where region 109 is made of germaniumtelluride, temperature T2 is for example equal to approximately 700° C.and duration d2 is for example equal to approximately 100 ns.

Switch 100 is said to be “indirectly heated”, the temperature rise ofthe phase-change material being obtained by the flowing of a currentthrough an electrically-heating element insulated from the phase-changematerial, as opposed to switches of “directly heated” type, whichcomprise no heating element and where the temperature rise results froma current flow directly through the phase-change material. In the caseof a directly heated switch, the control electrodes are for exampleconnected to two opposite sides of the region of phase-change material,for example, along a direction orthogonal to the conduction path of theswitch. A disadvantage of directly heated switches lies in the factthat, when the switch is on, an electric conduction path is createdthrough the phase-change material between the control electrodes and theconduction electrodes of the switch. This causes leakage currents, whichdisturb the signal transmitted between the conduction electrodes.

To respond to the constraints of various applications, for example inthe field of radio frequency communications, it is desirable for switch100 to have the lowest possible figure of merit. In the presentdisclosure, the figure of merit of a switch corresponds to a product ofan on-state resistance R_(ON) by an off-state capacitance C_(OFF) ofthis switch.

The on-state resistance R_(ON) of the switches of the present disclosureis defined by the following relation:

$\begin{matrix}{R_{ON} = {\frac{1}{\sigma_{ON}} \cdot \frac{L}{T \cdot W}}} & \left\lbrack {{Math}1} \right\rbrack\end{matrix}$

In the above relation Math 1, L, W, and T respectively designate thelength, the width, and the thickness of region 109 of phase-changematerial, length L and width W corresponding to dimensions of region 109measured along directions respectively parallel and orthogonal to theconduction direction of the switch, and cro N designates a conductivityof the phase-change material (expressed in Siemens per meter) when thelatter is in its crystal phase.

To decrease the figure of merit of switch 100, its on-state resistanceR_(ON) may for example be decreased by increasing the thickness T ofregion 109 of phase-change material. This would however cause anundesirable increase of switching durations, or a decrease in theswitching speed, between the on and off states. Indeed, for a samecontrol voltage, the thicker region 109 is, the longer the durations d1and d2, respectively corresponding to the durations of transitionbetween the amorphous phase and the crystal phase and between thecrystal phase and the amorphous phase. To decrease durations d1 and d2,one may be tempted to increase the control voltage of heating element113 but this would cause an undesirable increase in the energyconsumption of switch 100.

FIG. 3 is a partial and simplified perspective view of an example of aswitch 300 based on a phase-change material according to an embodiment.FIG. 4 is a cross-section view along plane AA of FIG. 3 , of the switch300 of FIG. 3 . The switch 300 of FIGS. 3 and 4 comprises elementscommon with the switch 100 of FIGS. 1 and 2 . These common elements willnot be detailed again hereafter.

According to an embodiment, switch 300 comprises one or a plurality ofpillar(s) 301 (several tens of pillars 301, in the shown example)extending in region 109 of phase-change material. More precisely, in theexample illustrated in FIGS. 3 and 4 , pillars 301 extend verticallythrough the entire thickness T of region 109.

According to an embodiment, pillar(s) 301 are made of a material havinga thermal conductivity greater than that of the phase-change material ofregion 109. As an example, pillars 301 are made of an electricallyinsulating and thermally conductive material, for example, siliconnitride, aluminum nitride, etc. As a variant, pillars 301 may be made ofan electrically and thermally conductive material, for example, a metal.However, for an implementation of switch 300 in radio frequencycommunication applications, the use of pillars 301 made of anelectrically insulating material is preferred to limit or to avoid theoccurrence of parasitic capacitive phenomena.

In the shown example, pillars 301 each have, in top view, asubstantially circular cross-section. This example is however notlimiting, and pillar(s) 301 may have any shape, for example, across-section of rectangular or square shape. As an example, each pillar301 has a maximum lateral dimension (for example, a diameter, in theshown example where the pillars have a substantially circularcross-section) equal to approximately 300 nm. Further, each pillar 301is for example separated from the neighboring pillars 301 by a distancein the order of 300 nm. Pillars 301 are for example distributedaccording to a periodic pattern. Although an example where switch 300comprises a few tens of pillars 301 has been described, switch 300 maycomprise any number of pillars 301.

An advantage resulting from the presence of pillars 301 lies in the factthat the heat generated by heating element 113 is more efficientlypropagated in region 109 of switch 300. In particular, as compared withswitch 100 having its region 109 mainly heated from its upper surface,the heat originating from the heating element 113 of switch 300 furtherdiffuses at the heart of the phase-change material of region 109. Switch300 thus has a thermal efficiency greater than that of switch 100.

In the case of switch 300, for a same control voltage applied betweenelectrodes 115 a and 115 b, heating element 113 undergoes, with respectto switch 100, a lower temperature rise. Further, for a same controlvoltage, region 109 of switch 300 undergoes, with respect to region 109of switch 100, a higher temperature rise. The differences between thetemperatures respectively reached by heating element 113 and by region109 during the switching steps is lower in the case of switch 300 thanin the case of switch 100.

For comparable thicknesses T of region 109, switch 109 enables to accessswitching durations shorter than, or to switching speeds greater than,those of switch 100. It is advantageously possible to take advantage ofthe increased thermal efficiency of switch 300 to increase thickness Tof region 109 with respect to switch 100, to decrease the figure ofmerit of switch 300, without degrading the switching durations withrespect to switch 100. Heating element 113 can further advantageously bedrawn away from region 109. This then causes a decrease in the off-statecapacitance C_(OFF), and thus a decrease in the figure of merit, ofswitch 300 with respect to switch 100.

The upper surface of region 109 of switch 300 may be, as in theillustrated example, integrally coated with an electrically insulatinglayer 303. Optional layer 303 for example enables to passivate the uppersurface of region 109. Layer 303 further enables to decrease theoff-state capacitance C_(OFF) of switch 300 with respect to switch 100,and thus to decrease the figure of merit of switch 300. In the shownexample, pillars 301 cross layer 303 across its entire thickness. Moreprecisely, in this example, each pillar 301 extends vertically from theupper surface of layer 303 to the lower surface of region 109. Layer 303for example has a thickness in the range from 200 to 300 nm. As anexample, layer 303 is made of silicon nitride or of germanium nitride(GeN).

In the illustrated example, switch 300 further optionally comprisesseparate electrically insulating regions 305 coating the upper surfaceof electrically insulating layer 107 and extending over a portion of theupper surface of each conduction electrode 105 a, 105 b. Each region 305for example has a thickness in the order of 20 nm. As an example,electrically insulating regions 305 are made of a dielectric material,for example, silicon nitride.

To avoid overloading the drawing, substrate 101, electrically insulatinglayers 103 and 107, and electrically insulating regions 305 have notbeen shown in FIG. 3 .

In the shown example, switch 300 further comprises an electricallyinsulating layer 307. The layer 307 of switch 300 is for example similarto the layer 111 of switch 100. In switch 300, layer 307 is interposedbetween layer 303 and heating element 113. More precisely, in theillustrated example, layer 307 coats the upper surface of pillars 301,the upper surface, and the sides of layer 303, the sides of region 109,the exposed portions of electrodes 105 a and 105 b, and the uppersurface and the sides of regions 305. As an example, layer 307 is madeof an electrically insulating and thermally conductive material, forexample, the same material as that of pillars 301, for example, siliconnitride or aluminum nitride.

Although this has not been illustrated in the drawings, the structure ofswitch 300 may be coated, on the upper surface side of substrate 101,with a thermally insulating layer intended to confine the heat generatedby heating element 113.

Switch 300 has a structure in which heating element 113 is more distantfrom substrate 101 than layer 109 of phase-change material. This impliesa low thermal capacity, heating element 113 being capable of beinglocated close to ambient air. This advantageously results in rapidthermal exchanges, and thus low switching durations.

FIG. 5 is a simplified and partial cross-section view of an example of aswitch 500 based on a phase-change material according to an embodiment.

The switch 500 of FIG. 5 comprises elements common with the switch 300of FIGS. 3 and 4 . These common elements will not be described againhereafter. Conversely to the switch 300 of FIGS. 3 and 4 , where region109 of phase-change material is located under heating element 113,region 109 of switch 500 is, in the orientation of FIG. 5 , locatedabove heating element 113.

In the shown example, heating element 113 is more precisely on top ofand in contact with the upper surface of electrically insulating layer103. Further, in this example, electrically insulating layer 307 coatsthe upper surface and the sides of heating element 113 and furtherextends on portions of the upper surface of layer 103 not coated withheating element 113.

In the example illustrated in FIG. 5 , region 109 of phase-changematerial, crossed by pillars 301, is located on top of and in contactwith the upper surface of layer 307, vertically in line with heatingelement 113. In this example, the conduction electrodes 105 a and 105 bof switch 500 are on top of and in contact with the upper surface oflayer 307. Further, electrodes 105 a and 105 b each coat a side and aportion of the upper surface of region 109.

In the shown example, electrically insulating layer 107 extends betweenelectrodes 105 a and 105 b. Layer 107 is, in the orientation of FIG. 5 ,on top of and in contact with the upper surface of region 109.

Although this has not been illustrated in FIG. 5 , switch 500 mayfurther comprise a layer of passivation of region 109 and electricallyinsulating layers respectively similar to layer 303 and to regions 305of the switch 300 of FIGS. 3 and 4 .

As compared with switch 300, switch 500 has a structure where heatingelement 113 is closer to substrate 101. This implies, in the case ofswitch 500, a higher thermal capacity which favors the application of alower control voltage on heating element 113, with respect to switch300, to obtain a comparable rise of the temperature of region 109 duringswitchings.

FIGS. 6A to 6C illustrate, in simplified and partial cross-sectionviews, successive steps of an example of a method of manufacturing theswitch 300 of FIG. 3 according to an embodiment.

FIG. 6A more precisely illustrates a step of forming of electricallyinsulating layer 103 on the upper surface of substrate 101, for example,by thermal oxidation of the material of substrate 101. FIG. 6A furtherillustrates a step of forming of conduction electrodes 105 a and 105 bon the upper surface of layer 103. As an example, a metallization levelis first deposited, for example, by physical vapor deposition (PVD) ofone or a plurality of metal layers, on the upper surface side ofsubstrate 101. Steps of photolithography and etching then enable to onlykeep portions of the metallization level which are located at thedesired locations of electrodes 105 a and 105 b. Radio frequency lines,not shown in FIG. 6A, may further be formed in the first metallizationlevel during this step.

FIG. 6B illustrates a step of forming of electrically insulating layer107 around electrodes 105 a and 105 b. As an example, layer 107 is firstdeposited, for example, by plasma-enhanced chemical vapor deposition(PECVD), for example, more precisely by high-density plasma-enhancedchemical vapor deposition (HDPCVD or HDP PECVD), on the upper surfaceside of the structure of FIG. 6A. Layer 107 may, after deposition, coatelectrodes 105 a and 105 b and have a thickness for example in the orderof 700 nm. A step of planarization, for example, by chemical mechanicalpolishing, then enables to expose the upper surfaces of electrodes 105 aand 105 b. Layer 107 for example then has a thickness substantiallyequal to that of electrodes 105 a and 105 b.

FIG. 6B further illustrates a step of forming of electrically insulatingregions 305. As an example, an electrically insulating layer is firstdeposited on the upper surface side of substrate 101. Steps ofphotolithography and etching then enable to keep portions of theelectrically insulating layer located at the desired locations ofregions 305. As a variant, regions 305 may be formed by local depositionof an electrically insulating material on the upper surface side ofsubstrate 101.

FIG. 6C illustrates a step of forming of region 109 of phase-changematerial and of passivation layer 303. As an example, a layer ofphase-change material and a passivation layer are successivelydeposited, for example, by physical vapor deposition, on the uppersurface side of the structure of FIG. 6B. Steps of photolithography andetching, for example, by reactive ion etching (RIE) or by ion beametching (IBE), then enable to only keep portions of the layer ofphase-change material and of the passivation layer at the desiredlocations of region 109 and of layer 303. During these steps, openings601 may further be formed in the layer of phase-change material and inthe passivation layer at the desired locations of pillars 301. As avariant, openings 601 may be formed after steps of photolithography andetching subsequent to the steps of forming of region 109 and of layer303.

During another step, subsequent to the steps described in relation withFIG. 6C, openings 601 are integrally filled to form pillars 301.Electrically insulating layer 307 is then deposited over the entireupper surface of the structure. In the case where pillars 301 and layer307 are made of the same material, pillars 301 are for example formedduring the deposition of layer 307. Heating element 113 is then formedon top of and in contact with the upper surface of layer 307. Controlelectrodes 115 a and 115 b and pads 117 may further be formed during thestep of forming of heating element 113, for example, from a samemetallization level. At the end of these steps, the switch 300 of FIG. 3is obtained.

Those skilled in the art are capable of adapting the method ofmanufacturing the switch 300 described hereabove in relation with FIGS.6A to 6C to form switch 500.

FIG. 7 is a partial and simplified perspective view of an example of aswitch 700 based on a phase-change material according to an embodiment.FIG. 8 is a cross-section view, along plane AA of FIG. 7 , of the switchof FIG. 7 . Plane AA of FIG. 7 is substantially parallel to a conductiondirection of switch 700.

The switch 700 of FIGS. 7 and 8 comprises elements common with theswitch 100 of FIGS. 1 and 2 . These common elements will not be detailedagain hereafter.

To avoid overloading the drawing, substrate 101 and electricallyinsulating layers 103 and 107 have not been shown in FIG. 7 .

According to an embodiment, the switch 700 of FIGS. 7 and 8 comprisesone or a plurality of electrically insulating islands 701 (three islands701, in the shown example) each having a first surface (the lowersurface, in the orientation of FIGS. 7 and 8 ) extending on top of andin contact with the first and second conduction electrodes 105 a and 105b of switch 700. In switch 700, region 109 of phase-change materialextends over a portion of the sides and over a portion of a secondsurface (the upper surface, in the orientation of FIGS. 7 and 8 ),opposite to the first surface, of each island 701. More precisely, inthe shown example, region 109 coats a portion of the sides of islands701 which are substantially parallel to plane AA of FIG. 7 , that is,the sides of islands 701 extending along the conduction direction ofswitch 700. In the shown example, the heating element 113 of switch 700further extends, along a direction orthogonal to the conductiondirection of switch 700, on top of and in contact with a portion of theupper surface of region 109.

Islands 701 are made of a dielectric material or comprise a stack ofdielectric materials. As an example, islands 701 are made of anelectrically insulating and thermally conductive material, for example,a material having a thermal conductivity greater than that of thephase-change material of region 109, for example, aluminum nitride. Thisadvantageously enables to obtain a lower thermal resistance betweenheating element 113 and region 109. A “quenching” phenomenon occurringduring the transition of region 109 from the crystal phase to theamorphous phase is thus favored. As a variant, islands 701 may be madeof silicon dioxide.

In the example illustrated in FIG. 7 , each island 701 has an elongatedshape along the conduction direction of switch 700 and a cross-sectionof substantially trapezoidal shape, the first surface of each island 701having a surface area greater than the second surface area. The fact ofproviding islands 701 having a trapezoidal cross-section, the sides ofislands 701 thus being inclined, advantageously enables to facilitatethe coating of islands 701 with region 109 with respect to a case whereislands 701 would have vertical sides, perpendicular to the first andsecond surfaces. The example illustrated in FIG. 7 is however notlimiting, each island 701 being as a variant capable of having across-section of any shape, for example, rectangular or square. Islands701 are for example distributed at regular intervals along the heatingelement (113).

In the switch 700 of FIG. 7 , region 109 of phase-change material isdeveloped on a three-dimensional structure, or in relief, conversely toswitch 100 where region 109 is substantially planar. This advantageouslyenables to increase the width W of region 109 of phase-change materialand/or to decrease the outer dimensions of the switch.

More precisely, switch 700 may have, as compared with switch 100, ashorter distance between its control electrodes 115 a and 115 b whilekeeping a region 109 having a width W substantially equal to that ofregion 109 of switch 100. This advantageously enables switch 700 to havesmaller outer dimensions, and thus a higher integration density, ascompared with switch 100.

As an example, in a case where switch 700 comprises two islands 701having a height in the order of 5 μm, a width, corresponding to anaverage lateral dimension of island 701 measured along a directionperpendicular to plane AA of FIG. 7 (direction parallel to the axis ofheating element 113), in the order of 1 μm and a spacing in the order of1 μm, the width W of region 109, developed on the three-dimensionalstructure, is in the order of 25 μm Switch 700 has in this case a width,substantially corresponding to a dimension of conduction electrodes 105a and 105 b taken orthogonally to plane AA of FIG. 7 , in the order of 5μm. As a comparison, the width of switch 100 is in the order of 25 μm ina case where its region 109 has a width equal to approximately 25 μm.

As a variant, it may be provided for region 109 of switch 700 to have awidth W greater than that of region 109 of switch 100, while keeping adistance between electrodes 115 a and 115 b smaller than or equal to thedistance between electrodes 115 a and 115 b of switch 100. Thisadvantageously enables switch 700 to have a lower on-state resistanceR_(ON), and thus a lower figure of merit, as compared with switch 100.

As a variant, it may be provided for region 109 of switch 700 to have awidth W greater and a thickness T smaller than that of region 109 ofswitch 100, while keeping a comparable on-state resistance R_(ON). Thefact of decreasing the thickness T of region 109 advantageously enablesto obtain faster phase changes during switchings. Further, the decreaseof the thickness T of region 109 enables to obtain a phase-changematerial of better crystal and stoichiometric quality. Thereby, thephase changes of the material of region 109 advantageously require lessenergy. The thermal efficiency of switch 700 is thus improved withrespect to switch 100.

Another advantage of switch 700 lies in the fact that the presence ofislands 701 enables to decrease the off-state capacitance C_(OFF).Islands 701 more precisely enable to decrease a parasitic capacitance Cpbetween heating element 113 and the conduction electrodes 105 a and 105b of switch 700, due to the fact that each island 701 draws heatingelement 113 away from electrodes 105 a and 105 b. Off-state capacitanceC_(OFF) is further decreased, with respect to switch 100, in a casewhere the width of switch 700 is smaller than that of switch 100.

Another advantage of switch 700 lies in the fact that the presence ofislands 701 enables, for an identical width W, to decrease theinductance of heating element 113 with respect to the case of switch100. This seems to be due to the fact that the mutual inductance betweenadjacent vertical sections of heating element 113 becomes negative, thuscausing a decrease in the total inductance. An inductance decrease ofheating element 113 advantageously enables to reach higher switchingspeeds.

Although this has not been illustrated in FIGS. 7 and 8 , switch 700 maycomprise a passivation layer and insulating regions identical or similarto the passivation layer 303 and to the regions 305 of the switch 300 ofFIGS. 3 and 4 .

FIG. 9 is a partial and simplified perspective view of an example of aswitch 900 based on a phase-change material according to an embodiment.

The switch 900 of FIG. 9 comprises elements common with the switch 700of FIGS. 7 and 8 . These common elements will not be described againhereafter.

To avoid overloading the drawing, substrate 101 and electricallyinsulating layers 103 and 107 have not been shown in FIG. 9 .

The switch 900 of FIG. 9 differs from the switch 700 of FIGS. 7 and 8 inthat switch 900 comprises a single island 701 interposed between region109 of phase-change material and conduction electrodes 105 a and 105 b.

Switch 900 has, in cross-section view along plane AA of FIG. 9 , astructure similar to that previously discussed in relation with FIG. 8 .

In switch 900, island 701 has dimensions, in particular, a width, suchthat the majority of region 109 coats island 701. This advantageouslyenables to take heating element 113 further away from conductionelectrodes 105 a and 105 b, and thus to decrease the off-statecapacitance C_(OFF) of switch 800 with respect to switch 700.

FIG. 10 is a simplified and partial cross-section view of an example ofa switch 1000 based on a phase-change material according to anembodiment.

The switch 1000 of FIG. 10 comprises elements common with the switch 700of FIGS. 7 and 8 . These common elements will not be detailed againhereafter.

The switch 1000 of FIG. 10 differs from the switch 700 of FIGS. 7 and 8in that, in switch 1000, electrically insulating layer 111 extends overthe entire upper surface of the structure. In the shown example,electrically insulating layer 111 coats region 109 of phase-changematerial and islands 701 of dielectric material. More precisely, in thisexample, layer 111 coats the upper surface and the sides of region 109of phase-change material, portions of the upper surface of each island701 not coated with region 109, all the sides of each island 701,portions of the upper surface of each conduction electrode 105 a, 105 bnot coated with islands 701, and portions of the upper surface ofelectrically insulating layer 107 not coated with islands 701.

The fact of providing for layer 111 to cover the entire structureenables to simplify the manufacturing of switch 1000, particularly ascompared with switches 700 and 900.

FIG. 11 is a simplified and partial cross-section view of an example ofa switch 1100 based on a phase-change material according to anembodiment.

The switch 1100 of FIG. 11 comprises elements common with the switch 700of FIGS. 7 and 8 . These common elements will not be detailed againhereafter.

The switch 1100 of FIG. 11 differs from the switch 700 of FIGS. 7 and 8in that, in switch 1100, region 109 of phase-change material coats eachisland 701 of dielectric material and electrically insulating layer 111extends over the entire upper surface of the structure. More precisely,in the shown example, region 109 of phase-change material coats theupper surface and all the sides of each island 701 and further extendson top of and in contact with a portion of the upper surface of eachconduction electrode 105 a, 105 b of switch 1100. Further, in thisexample, layer 111 coats the upper surface and the sides of region 109of phase-change material, portions of the upper surface of eachconduction electrode 105 a, 105 b not coated with region 109, andportions of the upper surface of electrically insulating layer 107 notcoated with islands 701.

In switch 1100, the portion of region 109 extending on top of and incontact with conduction electrodes 105 a and 105 b advantageouslyprovides a better electric contact between region 109 of phase-changematerial and electrodes 105 a and 105 b than in switches 700, 900, and1000. This further enables to simplify the manufacturing of switch 1100,particularly as compared with switches 700, 900, and 1000. Those skilledin the art are capable of adapting the embodiments of the switches 1000and 1100 described in relation with FIGS. 10 and 11 to switchescomprising any number of islands 701.

FIGS. 12A and 12B illustrate, in simplified and partial cross-sectionviews, successive steps of an example of a method of manufacturing aswitch based on a phase-change material according to an embodiment, forexample, the switch 700 of FIG. 7 .

FIG. 12A more precisely illustrates a structure obtained at the end ofsuccessive steps of forming of electrically insulating layer 103, offorming of control electrodes 105 a and 105 b, and of deposition andplanarization of layer 107. These steps are for example implementedidentically or similarly to what has been previously discussed inrelation with FIG. 6A.

FIG. 12B illustrates a step of forming of islands 701 on the uppersurface side of the structure. As an example, an aluminum nitride layeror a stack comprising an aluminum nitride layer and a silicon dioxidelayer is first deposited, for example, by plasma-enhanced chemical vapordeposition (PECVD) on the upper surface side of the structure of FIG.12A. Steps of photolithography and etching then enable to only keepportions of the layer or of the stack which are located at the desiredlocations of islands 701.

During subsequent steps, the phase-change material is deposited on theupper surface side of substrate 101. An optional passivation layeridentical or similar to layer 303 of switch 300 may be deposited on thephase-change material to protect it against oxidation. Steps ofphotolithography and etching then enable to keep the phase-changematerial, and possibly the material of the optional passivation layer,at the desired location of region 109.

The deposition of layer 111 can then be performed, for example byforming a silicon nitride layer by plasma-enhanced chemical vapordeposition (PECVD) or an aluminum nitride layer by physical vapordeposition (PVD). In the case where electrically insulating layer 111coats electrodes 105 a and 105 b, openings may then be formed, forexample, by photolithography and etching, for example, reactive ionetching (RIE), in layer 111 to expose portions of the upper surface ofeach electrode 105 a, 105 b.

Heating element 113 may then be formed, for example, by a step ofdeposition of a metallization level on the upper surface side ofsubstrate 101, followed by steps of photolithography and etching. Duringthis step, conductive vias may further be formed in thepreviously-formed openings to recover the contacts of electrodes 105 aand 105 b of the switch.

Those skilled in the art are capable of adapting the method ofmanufacturing the switch 700 described hereabove in relation with FIGS.12A and 12B to form switches 900, 1000, and 1100.

The embodiments of switches 300 and 500 previously discussed in relationwith FIGS. 3 to 5 may be combined with the embodiments of switches 700,900, 1000, and 1100 of FIGS. 7 to 11 . More precisely, it may beprovided to form, in the region 109 of phase-change material of switches700, 900, 1000, and 1100, pillars identical or similar to the pillars301 of switch 300. The structure of switches 700, 900, 1000, and 1100may further be modified to obtain a structure similar to that of switch500, where heating element 113 is interposed between substrate 101 andconduction electrodes 105 a and 105 b. Those skilled in the art arecapable of adapting the method of manufacturing switch 700 describedhereabove in relation with FIGS. 12A and 12B to form these differentstructures.

FIGS. 13A to 13D illustrate, in simplified and partial cross-sectionviews, successive steps of an example of a method of manufacturing aswitch 1300 based on a phase-change material according to an embodiment.

Switch 1300 comprises elements common with the switch 100 of FIGS. 1 and2 . These common elements will not be detailed again hereafter.

FIG. 13A more precisely illustrates a structure obtained after steps offorming of electrically insulating layer 103, on the upper surface sideof substrate 101, of forming of conduction electrodes 105 a and 105 b,and of deposition and planarization of layer 107. These steps are forexample implemented as previously discussed in relation with FIGS. 6Aand 6B. Steps of forming of region 109 of phase-change material and ofpassivation layer 303 are then implemented, for example, as previouslydiscussed in relation with FIG. 6B.

FIG. 13B more precisely illustrates a structure obtained at the end of astep of deposition of electrically insulating layer 307 on the uppersurface side of the structure of FIG. 13A, followed by a step ofdeposition of another electrically insulating layer 1301 coating layer307. Layer 1301 is for example then planarized, for example, by chemicalmechanical polishing, to obtain a structure having a planar uppersurface. As an example, layer 1301 is made of silicon dioxide or ofaluminum nitride.

FIG. 13C more precisely illustrates a structure obtained at the end of astep of forming of a heating element 1303 on top of and in contact withthe upper surface of layer 307, vertically in line with region 109.Heating element 1303 is for example identical or similar to the heatingelement 113 of switch 100. During this step, an opening is for exampleformed in layer 1301, for example by photolithography and etching, atthe desired location of heating element 1303. The opening is thenintegrally filled with the material(s) of heating element 1303 afterwhich a step of planarization, for example, by chemical mechanicalpolishing, is implemented to obtain a structure having a planar uppersurface, heating element 1303 being flush with the upper surface oflayer 1301. A subsequent step of deposition of an electricallyinsulating layer 1305 on the upper surface side of the structure is thenimplemented. Layer 1305 more precisely coats the upper surface of layer1301 and the upper surface of heating element 1303. As an example, layer1305 is made of aluminum nitride.

FIG. 13D more precisely illustrates the structure of switch 1300obtained at the end of successive steps of forming of conductive vias1307, each vertically extending from the upper surface of layer 1305 tothe upper surface of one of the conduction electrodes 105 a, 105 b ofswitch 1300, of forming of another region 1309 of phase-change materialcoated with another passivation layer 1311, and of deposition of anelectrically insulating layer 1313 on the upper surface side of thestructure.

Conductive vias 1307 are for example formed by forming openings throughthe entire thickness of layers 1305, 1301, and 307 to expose a portionof the upper surface of each electrode 105 a, 105 b, for example, byphotolithography and etching, at the desired locations of vias 1307. Theopenings are then integrally filled with the material of conductive vias1307, and then a step of planarization, for example, by chemicalmechanical polishing, is implemented to obtain a structure having aplanar upper surface, conductive vias 1307 being flush with the uppersurface of layer 1305. As an example, conductive vias 1307 are made oftungsten.

Region 1309 and layer 1311 are for example formed as previouslydiscussed, for example, in relation with FIG. 6C, for region 109 andlayer 303. As an example, region 1309 and layer 1311 are respectivelymade of the same materials as region 109 and layer 303.

In the shown example, layer 1313 coats the upper surface and the sidesof layer 1311, the sides of region 1309, and portions of the uppersurface of layer 1305 not coated with region 1309. Layer 1313 forexample enables to passivate switch 1300 to protect it againstoxidation.

Regions 109 and 1309 of phase-change material are each connected to oneof conduction electrodes 105 a and 105 b by means of conductive vias1307, region 1309 being, in the orientation of FIG. 13D, located aboveregion 109. Heating element 1303, located between regions 109 and 1309,is electrically insulated from region 109 by layer 307 and from region1309 by layer 1305.

The regions 109 and 1309 of phase-change material of switch 1300 mayeach have a thickness twice smaller than the thickness T of layer 109 ofswitch 100 while enabling switch 1300 to keep an on-state resistanceR_(ON) substantially equal to that of switch 100. This advantageouslyenables regions 109 and 1309 to have a better crystal quality. The useof regions 109 and 1309 thinner than the region 109 of switch 100further advantageously enables switch 1300 to reach higher switchingspeeds, the surface of the phase-change material exposed to heatgenerated by the heating element being, in switch 1300, substantiallydoubled with respect to switch 100, for a comparable cumulated thicknessof phase-change material. This enables switch 1300 to have a betterenergy performance than switch 100, the energy necessary for the phasechange of the material of regions 109 and 1309 being lower.

FIGS. 14A and 14B illustrate, in simplified and partial cross-sectionviews, successive steps of an example of a method of manufacturing aswitch 1400 based on a phase-change material according to an embodiment.

FIG. 14A more precisely illustrates a structure obtained, for examplefrom the structure previously described in relation with FIG. 13C, aftersteps of forming, on top of and in contact with the upper surface oflayer 1305, of another region 1409 of phase-change material coated withanother passivation layer 1411, and of deposition of an electricallyinsulating layer 1413 on the upper surface side of the structure.

Region 1409 and layer 1411 are for example formed as previouslydiscussed, for example, in relation with FIG. 6C, for region 109 andlayer 303. As an example, region 1409 and layer 1411 are respectivelymade of the same materials as region 109 and layer 303.

As an example, layer 1413 is first deposited on the upper surface sideof the structure after the forming of region 1409 and of layer 1411.Layer 1413 may for example, after deposition, coat the sides of region1409 and the upper surface and the sides of layer 1411. A step ofplanarization, for example, by chemical mechanical polishing, thenenables to expose the upper surface of layer 1411. After planarization,layer 1413 is for example flush with the upper surface of layer 1411 asin the example illustrated in FIG. 14A.

FIG. 14B more precisely illustrates a structure obtained at the end of astep of forming of conductive vias 1415, each extending vertically fromthe upper face of layer 1413 to the upper surface of one of conductionelectrodes 105 a, 105 b, of a step of forming of other conductive vias1417, each extending vertically from the upper surface of layer 1411 tothe upper surface of region 1409 close to two opposite sides of region1409, of a step of forming of two conduction electrodes 1419 a and 1419b, respectively connected to conduction electrodes 105 a and 105 b, andof a step of deposition of an electrically insulating layer 1421 on theupper surface side of the structure.

Conductive vias 1415 are for example formed by forming openings throughthe entire thickness of layers 1413, 1305, 1301, and 307 to expose aportion of the upper surface of each electrode 105 a, 1 05 b, forexample, by photolithography and etching, at the desired locations ofvias 1415. The openings are then integrally filled with the material ofconductive vias 1415. Similarly, conductive vias 1417 are for exampleformed by forming openings through the entire thickness of layer 1411 toexpose portions of the upper surface of layer 1409, for example, byphotolithography and etching at the desired locations of vias 1417. Astep of planarization, for example, by chemical mechanical polishing, isfor example then implemented to obtain a structure having a planar uppersurface, conductive vias 1415 and 1417 being flush with the uppersurface of layer 1413. As an example, conductive vias 1415 and 1417 aremade of tungsten.

Electrodes 1419 a and 1419 b are for example formed similarly to whathas been discussed in relation with FIG. 6A for electrodes 105 a and 105b. Each of electrodes 1419 a, 1419 b is connected to the correspondingelectrode 105 a, 105 b by one of conductive vias 1415, and to region1409 by one of vias 1417. As an example, electrodes 1419 a and 1419 bare made of the same material, or comprise the same stack of layers ofmaterials, as electrodes 105 a and 105 b.

As an example, layer 1421 is deposited on the upper surface side of thestructure after the forming of electrodes 1419 a and 1419 b. Layer 1413may for example, after deposition, coat the upper surface and the sidesof electrodes 1419 a and 1419 b. A step of planarization, for example,by chemical mechanical polishing, then enables to obtain a structurehaving a planar upper surface.

Switch 1400 has advantages identical or similar to those of switch 1300.

Although there has been illustrated in relation with FIGS. 14A and 14Ban implementation mode of a method of manufacturing a switch comprisingtwo regions 109 and 1409 of phase-change material, those skilled in theart would be capable of adapting this method to form switches comprisinga number of regions of phase-change material greater than two, that is,a structure comprising an alternation of layers of phase-change materialand of heating elements. This would enable to further decrease thethickness of each region of phase-change material with respect to switch100 while keeping a similar on-state resistance R_(ON).

The embodiments of switches 1300 and 1400 previously discussed inrelation with FIGS. 13D and 14B may be combined with the embodiment ofthe switch 300 of FIG. 3 . In particular, it may be provided for one ofthe regions 109, 1309, 1409 of phase-change material of switches 1300and 1400 to comprise one or a plurality of pillars, similar to thepillars 301 of switch 300, extending in the region of phase-changematerial, the pillar(s) being made of a material having a thermalconductivity greater than that of the phase-change material. Switches1300 and 1400 would thus benefit from advantages similar to those ofswitch 300.

The embodiments of the switches 1300 and 1400 previously discussed inrelation with FIGS. 13D and 14B may further be combined with theembodiments of the switches 700, 900, 1000, and 1100 of FIGS. 7, 9, 10,and 11 . In particular, it may be provided for at least one of theregions 109, 1309, 1409 of phase-change material of switches 1300 and1400 to be developed on a three-dimensional surface comprising at leastone island identical or similar to islands 701.

Those skilled in the art are capable of adapting the method ofmanufacturing the switch 1300 described hereabove in relation with FIGS.13A to 13D and the method of manufacturing the switch 1400 describedhereafter in relation with FIGS. 14A and 14D to form these differentstructures.

Various embodiments and variants have been described. Those skilled inthe art will understand that certain features of these variousembodiments and variants may be combined, and other variants will occurto those skilled in the art.

Finally, the practical implementation of the described embodiments andvariants is within the abilities of those skilled in the art based onthe functional indications given hereabove. In particular, the describedembodiments are not limited to the specific examples of materials and ofdimensions mentioned in the present disclosure.

Switch (300; 500) based on a phase-change material may be summarized asincluding a region (109) of said phase-change material; a heatingelement (113) electrically insulated from the region of saidphase-change material; and one or a plurality of pillars (301) extendingin the region of said phase-change material, the pillar(s) being made ofa material having a thermal conductivity greater than that of saidphase-change material.

The material of the pillar(s) (301) may be electrically insulating.

The material of the pillar(s) (301) may be selected from aluminumnitride and silicon nitride.

Said phase-change material may be a chalcogenide material.

An electrically insulating layer (307) may be interposed between theheating element (113) and the region (109) of said phase-changematerial.

The electrically insulating layer (307) may be made of the same materialas the pillar(s) (301).

The region (109) of said phase-change material may be closer to asubstrate (101), inside and on top of which is formed the switch (300),than the heating element (113).

The heating element (113) may be closer to a substrate (101), inside andon top of which is formed the switch (500), than the region of saidphase-change material.

The region (109) of said phase-change material may be coated with apassivation layer (303).

The region (109) of said phase-change material may couple first andsecond conduction electrodes (105 a, 105 b) of the switch (300; 500).

Each pillar (301) may have a maximum lateral dimension equal toapproximately 300 nm.

Each pillar (301) may be separated from the neighboring pillars (301) bya distance in the order of 300 nm.

The various embodiments described above can be combined to providefurther embodiments. Aspects of the embodiments can be modified, ifnecessary to employ concepts of the various patents, applications andpublications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A switch based on a phase-change material, comprising: a region ofthe phase-change material; a heating element electrically insulated fromthe region of the phase-change material; and a plurality of pillarsextending in the region of the phase-change material, the pillars beingmade of a material having a thermal conductivity greater than that ofthe phase-change material.
 2. The switch according to claim 1, whereinthe material of the pillars is electrically insulating.
 3. The switchaccording to claim 1, wherein the material of the pillars is selectedfrom aluminum nitride and silicon nitride.
 4. The switch according toclaim 1, wherein the phase-change material is a chalcogenide material.5. The switch according to claim 1, wherein an electrically insulatinglayer is interposed between the heating element and the region of thephase-change material.
 6. The switch according to claim 5, wherein theelectrically insulating layer is made of the same material as thepillars.
 7. The switch according to claim 1, wherein the region of thephase-change material is closer to a substrate, inside and on top ofwhich is formed the switch, than the heating element.
 8. The switchaccording to claim 1, wherein the heating element is closer to asubstrate, inside and on top of which is formed the switch, than theregion of the phase-change material.
 9. The switch according to claim 1,wherein the region of the phase-change material is coated with apassivation layer.
 10. The switch according to claim 1, wherein theregion of the phase-change material couples first and second conductionelectrodes of the switch.
 11. The switch according to claim 1, whereineach pillar has a maximum lateral dimension equal to approximately 300nm.
 12. The switch according to claim 1, wherein each pillar isseparated from the neighboring pillar by a distance in the order of 300nm.
 13. A device, comprising: a phase-change material switch thatincludes: a region of phase-change material; a heating element on thephase-change material; and a plurality of pillars extending in theregion of the phase-change material.
 14. The device of claim 13 whereinthe plurality of pillars are a material having a thermal conductivitygreater than that of the phase-change material.
 15. The device of claim14 wherein the switch includes a first electrode spaced from a secondelectrode, the region of phase change material being on the first andsecond electrodes.
 16. The device of claim 15 wherein the switchincludes a first insulating layer between the first electrode and theregion of phase change material.
 17. A device, comprising: a substrate;a first electrode on the substrate; a second electrode on the substrate;a phase change material on the first and second electrodes; a pluralityof pillars in the phase change material, the plurality of pillarsincluding a material that is different from the phase change material.18. The device of claim 17 wherein the material of the plurality ofpillars have a thermal conductivity greater than that of thephase-change material.
 19. The device of claim 18, comprising a heatingelement on the phase change material.